If you're just asking for the best and not what someone given X stats could do, runecrafting, herblore and crafting are some of the best.
You can buy uncut dragonstones 60-70k, cut, add a gold bar and ball of wool then you've got a glory you can sell for around 70-80k.
Runecrafting, pretty self explanatory. Everyone needs laws & natures.
Herblore, you can make a fair bit if you get the right prices and it's quite rapid to make, you've just got to hunt down the secondaries and herbs for awhile.